Add `unsafe` keyword to unsafe block in rust code (#18264)

Closes #18264

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/18264 from tempoz:tempoz-fix-unsafe-block-rust aca540fac9
PiperOrigin-RevId: 676912529

src/google/protobuf/compiler/rust/message.cc

@@ -285,21 +285,36 @@ void UpbGeneratedMessageTraitImpls(Context& ctx, const Descriptor& msg) {
       unsafe impl $pbr$::AssociatedMiniTable for $Msg$ {
         #[inline(always)]
         fn mini_table() -> *const $pbr$::upb_MiniTable {
-          $std$::ptr::addr_of!($minitable$)
+          // This is unsafe only for Rust 1.80 and below and thus can be dropped
+          // once our MSRV is 1.81+
+          #[allow(unused_unsafe)]
+          unsafe {
+            $std$::ptr::addr_of!($minitable$)
+          }
         }
       }
 
       unsafe impl $pbr$::AssociatedMiniTable for $Msg$View<'_> {
         #[inline(always)]
         fn mini_table() -> *const $pbr$::upb_MiniTable {
-          $std$::ptr::addr_of!($minitable$)
+          // This is unsafe only for Rust 1.80 and below and thus can be dropped
+          // once our MSRV is 1.81+
+          #[allow(unused_unsafe)]
+          unsafe {
+            $std$::ptr::addr_of!($minitable$)
+          }
         }
       }
 
       unsafe impl $pbr$::AssociatedMiniTable for $Msg$Mut<'_> {
         #[inline(always)]
         fn mini_table() -> *const $pbr$::upb_MiniTable {
-          $std$::ptr::addr_of!($minitable$)
+          // This is unsafe only for Rust 1.80 and below and thus can be dropped
+          // once our MSRV is 1.81+
+          #[allow(unused_unsafe)]
+          unsafe {
+            $std$::ptr::addr_of!($minitable$)
+          }
         }
       }
     )rs");